1. Field of the Invention
The invention relates to a curve path of a switch comprising switch tongues, a main track and a branch track, which curve path from the beginning of the curve path to the end of the curve path is comprised of several portions having different curvatures 1/R, R being the radius of curvature.
2. Prior Art
From the article in ETR 39 (1990), H.1/2, January/February, by Reimar Holzinger and Dieter Fritz, xe2x80x9cEntwicklung moderner Hochleistungsweichen zur Wahrung der Zukunftschancen der Bahnxe2x80x9d, a number of switch geometries have become known for meeting the demands of high-speed traffic, which, as a rule, are characterized by a high degree of symmetry in order to prevent sudden changes in direction or curvature of the track and hence excessive transverse accelerations. The considerations made in that article relate to transition curves of the clothoid and cosine parabola types and sinus transition curves, changes in acceleration (jerks) being contemplated in detail.
From WO 95/31604 a curve path for the course of rails from the main track to a branch track can be taken, in which, likewise departing from a first end portion starting with a radius of curvature towards infinity, the respectively other end of the switch is again configured with a radius ending towards infinity in order to avoid additional vibratory excitations that may have adverse effects on vehicles. In that known configuration, a curve path comprised of three portions has been chosen, three approximately equally long portions being used. Departing from a curvature having a radius of curvature tending towards infinity, a central portion having a constant curvature whose radius constitutes a minimum over the curve path is chosen. In the main, this results in the course of two conventional clothoids having an intermediate portion in the form of a circular arc.
The invention aims at providing a curve path of the initially defined kind, which entails less wear of the structural components and hence higher service lives as well as lower overall costs, in particular in high-speed operation. At the same time, the invention aims to improve the maintenance expenditures and travelling comfort of such switches, in particular high-speed switches. To solve this object, the curve path of a switch according to the invention essentially consists in that the coefficient of curvature xcex1=1/R/1/Rmin at the beginning of the curve path (xcex1A) and at the end of the curve path (xcex1E) is selected to be xe2x89xa70 and that the point, or a region, in which xcex1=1 is located at a relative distance xcexd=L/Lgesxe2x89xa00.5 from the beginning of the curve path, L being the distance from the beginning of the curve path and Lges being the length of the curve path. The curvature 1/R serves to define a dimensionless coefficient of curvature xcex1, which equals the quotient of the instantaneous curvature 1/R and the maximum curvature 1/Rmin, the maximum curvature, in turn, resulting from the quotient of 1 and the minimum radius. xcex1can, thus, assume values of between 0 and 1, hence the radius is tending towards infinity in points in which xcex1 equals zero, since the minimum radius has a finite value. In the point of maximum curvature, and hence of minimum radius, this coefficient xcex1 assumes the value 1. In addition to defining the value xcex1, also a coefficient xcexd is defined, which sets the respective distance between the beginning of the curve path and the curve path point considered in relation to the total length of the curve path. The value xcexd, thus, equals zero at the beginning of the curve path and 1 at the end of the curve path, assuming any values of between 0 and 1 in direct proportion to the distance from the beginning of the curve path. Investigations into vehicle movement dynamics, under consideration of the usual course of cross sectional changes of the structural elements concerned, such as, e.g., tongue and nose of crossing, have now proved that, by turning away from the usual symmetry in the structure of such curve paths, it is feasible to both reduce wear and enhance comfort by the point or region with xcex1=1 being located at a relative distance xcexdxe2x89xa00.5 from the beginning of the curve path.
It has now been shown that the curve path geometry may be further optimized to the extent that the moving direction in which the switch is usually travelled over is also taken up into geometry considerations. With a particular advantage, xcex1A and xcex1E are selected between 0 and 0.5 and xcexdmax for xcex1max between 0.45 and 0.8 and unequal to 0.5 for a bidirectionally passed switch. A bidirectionally passed switch means that the switch is travelled over both facing and trailing. A switch travelled over primarily in one direction in a particularly advantageous manner is designed such that, for a switch passed facing, xcex1A is selected between 0 and 0.5, xcex1E is selected between 0.5 and 1 and xcexd for xcex1max is selected between 0.4 and 1 and unequal to 0.5 and that, for a switch passed trailing, xcex1A is selected between 0.3 and 0.7, xcex1E is selected between 0 and 0.5 and xcexd for xcex1max is selected between 0.3 and  less than 0.5. The values indicated above for the different curve path geometries for different travelling directions have been optimized in terms of minimum lateral accelerations and running-in jerks as well as slight wear phenomena and small wheel-rail forces. A slight lateral acceleration and break-in jerk thereby guarantee a high comfort in passing the switch, little wear and small wheel-rail forces render feasible a long service life of the switch.
In a particularly advantageous manner, the configuration according to the invention is devised such that one, and only one, point of maximum curvature or minimum radius with xcexdxe2x89xa00.5 is provided between the beginning of the curve path and the end of the curve path. Here again, the turning away from the hitherto chosen symmetry as suggested, for instance, in WO 95/31604, brings about a substantial improvement in comfort and a reduced wear. If one, and only one, point of maximum curvature is provided, the curve path geometry may have the form of a vertex clothoid in the curved course, wherein xcexd will assume a value of xe2x89xa00.5 in accordance with the definition chosen above, if such a vertex clothoid is used. In the case of cosinoids, it is known to select different values xcex1 at the beginning of the curve path and at the end of the curve path, wherein it has hitherto been common also in that case to select the value xcex1 at the end of the curve path to be 0 and, thus, progressively merging into the connection rail. If, as in accordance with a preferred further development of the invention, an intermediate region is chosen instead of one, and only one, point of maximum curvature, the configuration advantageously is devised such that a portion of constant maximum curvature is arranged between the beginning of the curve path and the end of the curve path, wherein the radius constitutes a minimum and whose center is arranged outside the center between the beginning of the curve path and the end of the curve path, the symmetry considerations made so far again having been left in the instant case. The central region of such a circular arc portion, like the previously mentioned one, and only one, point of maximum curvature, is not located in the longitudinal center of the curve path, thereby offering improvements in terms of wear and moving comfort.
In a particularly simple manner, the configuration is devised such that the portions differing from the shape of a circular arc are formed by clothoids and/or cosinoids. If, as already pointed out above, the travelling direction is additionally taken up into the switch geometry considerations, the curve path geometry in a particularly advantageous manner is defined such that, with a switch passed facing, the point of maximum curvature is arranged at the end of the curve path. In case of vertex clothoids and cosinoids, one, and only one, point of maximum curvature is usually observed, wherein in those cases the configuraton is devised such that the point of maximum curvature is arranged closer to the beginning of the curve path with vertex clothoids or cosinoids, in particular when trailing a switch.
As already mentioned in the beginning, the curve path according to the invention is suitable, in particular, for the construction of track connections aimed to be passed at high speeds. A track connection according to the invention using switches of the initially defined kind travelled over in both directions preferably is designed in a manner that the curve path ends merge into a straight-line connecting portion with xcex1E ranging between 0 and 0.5. The track connection in a particularly preferred manner is devised such that the straight-line portion has a length of from 5 to 30% of the total length Lges of a curve path. This straight-line connecting portion at a ratio of 5 to 30% of the total length of a curve path provides for a substantially enhanced steadiness of the run of the vehicle.
The switch geometries according to the invention, thus, are primarily applicable to track connections travelled over at high speeds, whereby the combination of different switch geometries according to the invention, as defined above, guarantees a substantially reduced wear and a substantially enhanced service life.